U.S. patent number 4,570,610 [Application Number 06/687,519] was granted by the patent office on 1986-02-18 for pulse combustion burner for cooking surface.
This patent grant is currently assigned to Gas Research Institute. Invention is credited to Robert L. Himmel.
United States Patent |
4,570,610 |
Himmel |
February 18, 1986 |
Pulse combustion burner for cooking surface
Abstract
A closed top pulse combustion burner for a flat cooking surface.
The burner comprises a shallow rectangular box-like combustion
chamber with its top providing a cooking surface area. Pulse
combustion operation of the burner promotes high thermal
efficiency. An internal baffle arrangement in the burner box
provides a high degree of temperature uniformity at the cooking
surface. The rectangular configuration of the burner unit allows
modular construction of multiple burner units which can be
individually operated at different times and/or temperatures.
Inventors: |
Himmel; Robert L. (Cleveland,
OH) |
Assignee: |
Gas Research Institute
(Chicago, IL)
|
Family
ID: |
24760735 |
Appl.
No.: |
06/687,519 |
Filed: |
December 28, 1984 |
Current U.S.
Class: |
126/39E; 99/422;
99/447; 126/39K; 126/214D; 431/1; 126/39H; 126/39R; 126/214R |
Current CPC
Class: |
F24C
3/085 (20130101); F23C 15/00 (20130101); Y02B
40/00 (20130101); Y02B 40/166 (20130101) |
Current International
Class: |
F23C
15/00 (20060101); F24C 3/08 (20060101); F24C
003/00 () |
Field of
Search: |
;126/39D,39R,39E,39H,39N,39J,39K,214A,214R,214D ;431/1
;99/422,447 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Green; Randall L.
Attorney, Agent or Firm: Pearne, Gordon, Sessions, McCoy,
Granger & Tilberry
Claims
What is claimed is:
1. A cooking appliance having a flat cooking surface and a pulse
combustion burner for heating the cooking surface, the burner
comprising a closed shallow combustion chamber formed by
intersecting walls, a top of the combustion chamber being in heat
transfer relation to the cooking surface, an inlet aperture in a
wall of the combustion chamber, gas valve means for supplying a
flow of combustible gas to the combustion chamber through the inlet
aperture means and restricting reverse flow, means for igniting the
combustible gas delivered to the combustion chamber by the gas
valve means, outlet aperture means in a wall of the combustion
chamber, tailpipe means connected to the outlet aperture means for
receiving combusted gases from the combustion chamber, and baffle
means in said combustion chamber to shield an area of the
combustion chamber associated with the cooking surface adjacent
said inlet means from excessive heat transfer from a primary
combustion zone immediately upstream of said inlet aperture
means.
2. An appliance as set forth in claim 1, wherein said baffle means
includes means to direct flow of combustion gases around peripheral
areas of the combustion chamber.
3. A cooking appliance having a flat cooking surface, a pulse
combustion burner for heating the cooking surface, the burner
comprising a closed shallow box combustion chamber having bottom,
side and top walls, the top wall being formed by a plate providing
said cooking surface at its upper side, a mixer head communicating
with the combustion chamber through an inlet aperture generally
centrally disposed in the bottom combustion chamber wall, gas valve
means for supplying combustible gases to the mixer chamber and
preventing reverse flow through such valve means, means for
igniting combustible gases supplied to the mixer head, tailpipe
means communicating with the combustion chamber through exhaust
port means in the bottom wall of the combustion chamber adjacent
one of the sides of the combustion chamber, and baffle means
overlying the inlet aperture, said baffle means being arranged to
shield the central region of the combustion chamber top wall from
direct exposure to a primary combustion zone at said inlet aperture
and promoting flow of combustion gases away from said inlet
aperture first towards a side of said combustion chamber opposite
said exhaust port means and then peripherally of said combustion
chamber and then towards said exhaust port means.
4. An appliance as set forth in claim 3, wherein said baffle means
comprises a generally rectangular box substantially centrally
disposed within said combustion chamber.
5. An appliance as set forth in claim 4, wherein said baffle box
has a restricted opening in a side adjacent said exhaust port means
and has a generally fully open side remote from said exhaust port
means.
6. An appliance as set forth in claim 5, wherein a top of said
baffle box is vertically spaced a limited distance from the top
wall of said combustion chamber.
Description
BACKGROUND OF THE INVENTION
The invention relates to closed top burners for cooking surfaces
and in particular to a burner of this type that employs pulse
combustion operation.
PRIOR ART
Commercial fuel fired closed top cooking surfaces such as those
used in restaurants, fast food outlets and the like commonly employ
Bunsen-type burners arranged to heat the underside of the cooking
surface. Efficiency of these conventional atmospheric burners is
inherently limited by their requirement of substantial quantities
of excess air needed for full combustion. Standby thermal losses
occur when such a burner is not in operation and natural convection
currents carry heat away from its surfaces and/or its environment.
Additional thermal losses can occur when a power ventilation hood
is operated over a burner of this type and hot gases are drawn from
its heated surface areas.
SUMMARY OF THE INVENTION
The invention provides a pulse combustion burner for closed top
cooking surfaces of commercial ranges, griddles, fry tops and the
like which achieves a high thermal efficiency and a high degree of
temperature uniformity across the cooking surface. The pulse
combustion process occurring in the burner develops a positive flow
of gas through a closed combustion chamber. Pressure pulses in the
combustion gases create a high degree of turbulence in the burner
which is effective to scrub off stagnant gas layers from the
internal burner surfaces and thereby achieve high heat transfer
with the cooking surface. Since the burner does not rely on natural
convection currents for discharge of combustion product gases,
thermal losses through the burner during standby or off periods are
effectively avoided. Since the combustion chamber of the burner is
entirely closed operation of a ventilation hood in the cooking area
cannot pull off significant quantities of useful hot gases from the
combustion area. A fuel savings of 25% can be achieved with use of
a burner of the present invention as compared to the use of
conventional atmospheric burners.
As disclosed, the combustion chamber of the burner is in the form
of a shallow box with its top formed by a plate which serves as the
cooking surface. A mixing head admits combustion gases to the
bottom center of the combustion chamber box while combustion
products exit through a pair of exhaust pipes connected near a
bottom edge of the box. A baffle within the combustion chamber box
shields a potentially hot central area of the cooking plate and
induces hot gases to flow through potentially cool peripheral areas
of the cooking plate. Preferably, the burner box is square or
otherwise of simple rectangular shape in plan view. This
rectangular modular configuration offers flexibility in product
design wherein the burner can be combined in multiple units for
heating a relatively large cooking surface. In such a case one or
more burner units can be selectively operated depending on the size
and/or temperature of the cooking surface needed at a particular
time.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a commercial flat top cooking
surface constructed in accordance with the invention;
FIG. 2 is a fragmentary isometric view of the underside of a
typical one of the burners of the range of FIG. 1;
FIG. 3 is a fragmentary isometric view of the upper side of the
typical range burner;
FIG. 4 is a vertical cross-sectional view taken along the line 4--4
indicated in FIG. 3 of the typical burner;
FIG. 5 is a schematic cross-sectional view of an air valve; and
FIG. 6 is a schematic cross-sectional view of a gas valve.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings there is shown a commercial flat top
cooking appliance 10 suitable for cooking and like use in a
restaurant, fast food outlet or other high use facility. In the
illustrated case, the appliance 10 has a plurality of closed top
burners 11 arranged in a rectangular array. The burners 11, which
are substantially identical, are mounted on a common rectangular
horizontal plate 12 formed of 5/8" steel stock, for example. An
upper face 13 of the plate provides the cooking surface of the
range. The nominal size of each of the illustrated burners 11, in
plan view, is one foot square so that with the burners arranged in
a two by three array, the plate 12 is approximately 2' by 3' in its
planar dimensions. The plate 12 is supported at convenient counter
height by a frame 14 fabricated of steel angle stock. The frame 14
can be covered with suitable cabinetry.
A typical burner 11 has the general form of a shallow square box
with four sides 16 and a bottom 17. The panels forming the sides 16
and bottom 17 are fabricated of 1/8" cold roll steel, for example.
The sides 16 and bottom 17 are joined together in an air tight
manner such as by welding. An overlying portion of the cooking
plate 12, which forms the top of the burner box, is joined to these
burner box sides 16 also in an air tight manner such as by
continuous welding. The upper side of the burner bottom panel 17 is
covered with a layer of thermal insulation 18 such as ceramic fiber
paper marketed under the registered trademark Fiberfrax. The lower
exterior side of the burner panel 17 can be covered with fiberglass
batting insulation (not shown).
Centrally located on the burner bottom panel 17 is a gas mixer head
21 conveniently formed, for example, by 11/2" steel pipe seal
welded at one end to the bottom panel and closed off at its other
end by a steel plate. The mixer head 21 forms an internal chamber
22 that is open to the interior of the burner box 11 through a
central inlet aperture 23 in the bottom panel 17. This aperture 23
is equal in size to the inside diameter of the chamber 22 and
allows free passage of gas from the chamber. Fuel, such as natural
gas, is delivered from a source (not shown) through a one way or
flapper valve 26. The valve 26 is connected to the mixer chamber 22
through a pipe coupling 27 seal welded to the mixer head 21 at a
port 28 through the sidewall of the head 21. The gas valve 26,
illustrated in FIG. 6, is of a generally known construction and
operation. Pressure of the gas supply, typically in the order of
11/2 to 2" of water column, displaces a thin gas impervious annular
membrane 24 from a wall 25 to uncover ports 30 and allow fuel gas
flow in the direction of the arrows into the mixing chamber 22.
Pressure pulses occurring during combustion in the mixing chamber
22 cause the membrane or flapper 24 to seat against the wall 25 and
prevent return flow of gas through the ports 30. A gas decoupler
chamber 29 is disposed in the gas supply circuit upstream of the
flapper valve 26.
Air is delivered to the mixing chamber 22 through a one way flapper
valve 31 connected to a pipe nipple 32 seal welded to the mixer
head 21 at a port 34 through the mixing chamber sidewall. The air
valve 31 is diagrammatically illustrated in FIG. 5. Air is admitted
into the interior of the valve 31 through a plurality of apertures
33 in an end wall 35. During operation of the burner 11,
sub-atmospheric pressure pulses are created and a flapper membrane
38 allows air to flow through the apertures 33 into the valve 31.
Reverse air flow during positive phases of the pressure pulses is
prevented by seating of the membrane 38 against the wall 35. A
spark plug 36 is received in an internally threaded boss 37 formed
on the sidewall of the mixer head 21 and projects into the chamber
22 for igniting gas therein.
Adjacent a pair of adjoining corners of the bottom panel 17 are a
pair of exhaust ports 41. The ports 41 are circular apertures which
communicate with pipe couplings 42, in the illustrated case 1/2"
pipe couplings, seal welded at the lower surface of the bottom
panel 17. The exhaust ports or apertures 41 have a diameter
substantially equal to the inside diameters of the couplings 42. A
separate tailpipe 43 is connected to each of the exhaust port
couplings 42. In the illustrated case, these tailpipes are 1/2"
standard steel pipe approximately 22" in length.
A baffle 51 shrouds the gas inlet opening or aperture 23 in the
burner box 11. The baffle 51 has the general configuration of a
shallow square box horizontally centered within the burner box 11.
An upper side 52 of the baffle box 51 is imperforate and is spaced
slightly, for example 1/8" from the underside of the cooking plate
12. A lower side of the baffle box 51 is formed by the central
region of the lower or bottom burner panel 17 and insulation layer
18. A vertical end wall 53 of the baffle box 51 adjacent the
exhaust ports 41 comprises two sections 53a, 53b spaced by a
rectangular opening 54. A pair of opposed imperforate walls 56
forming the sides of the baffle box 51 extend perpendicularly from
the plane of these spaced sections 53a, 53b. A side of the baffle
box 51 opposite the spaced sections 53a, 53b is substantially
completely open.
In use of the appliance 10, one or more of the burners 11 is
operated depending on the cooking surface area and/or distinct
temperature levels required at a particular time. For each burner
11, suitable controls responsive to a thermostat sensing the
temperature of the area of the cooking plate 12 associated with
such burner supply natural gas or other fuel to its flapper valve
26. The controls also energize the spark plug 36 to initiate
combustion in the mixer head chamber 22. A start-up blower and
suitable ducting (not shown) can be provided to direct a temporary
blast of air towards the air valve end wall 35 to purge the air
valve 31 and otherwise promote favorable burner starting
conditions.
Once initiated, combustion occurs in cyclic pulses within a
combustion chamber 15 formed by the burner box 11. The combustion
chamber 15 and the tailpipes 43 operate as a quasi-Hemholtz
resonator. The combustion process is self supporting, once
initiated, so that any start-up blower and the spark plug 36 may be
de-energized. The combustion pulses generate positive pressure
waves in the combustion chamber 15 which are effective to expel
burned gases out of the combustion chamber through the tailpipes
43. The flapper valves 26, 31 permit the flow of gases only into
the mixer chamber 22 and restrict reverse flow through their
respective bodies.
The baffle 51 achieves a relatively high degree of temperature
uniformity on the overlying area of the cooking plate surface 13.
The upper plate or face 52 of the baffle 51 shields the central
zone of the overlying area of the plate 12 from direct impingement
of and radiation from the flame formed in the primary combustion
zone immediately adjacent the central aperture 23. At the same
time, this upper plate 52 and the baffle sides 56, 53 cooperate to
channel or direct hot combustion gases exiting the mixer chamber 22
horizontally away from the exhaust ports 41. The baffle end walls
53a, 53b by limiting the size of the intervening opening 54
restrict the volume of hot gases that can travel the relatively
shorter more direct path from the aperture 23 through the opening
54 to the exhausts 41.
The result of causing a significant volume of combustion gases to
follow the indirect route from the mixer head aperture 23 through
the fully open baffle side 58 remote from the exhaust ports 41 is
to develop uniform heating of the peripheral zones of the cooking
plate 12 overlying the burner box 11. By way of example, a burner
unit of the general construction described above has demonstrated a
relatively even temperature distribution across its upper surface
of + or -25.degree. F. from a set point of 350.degree. F.
The disclosed burner, which has a nominal rating of 10,000 BTU/hr.,
achieves a high degree of thermal efficiency in the order of 60% as
a result of the highly turbulent flow of gas through the combustion
chamber 15 which is incident to the rapidly changing flow rate
associated with pulse combustion. As can be understood from the
foregoing description, the combustion chamber 15 is completely
enclosed and this containment reduces the amount of hot gas which
can be drawn away from the burner by a ventilation hood overlying
the cooking appliance 10. It can also be understood that standby
losses, when the burner is not operating, are at a minimum since
natural drafts through the burner do not occur.
Although the preferred embodiment of this invention has been shown
and described, it should be understood that various modifications
and rearrangements of the parts may be resorted to without
departing from the scope of the invention as disclosed and claimed
herein.
* * * * *